Manufacture of alternating elec



Patented Sept. 12, 1939 UNITED STATES PATENT OFFICE MANUFACTURE OFALTERNATING ELEC- TRIO CURRENT RECTIFIERS Roger Harry Cubitt, London,England, assignor, by mesne assignments, to The Union Switch at SignalCompany, Swissvale, Pa., a corporation of Pennsylvania No Drawing.

Application November 12, 1937,

1855a! No. 174,181. .In Great Britain May 6,

3 Claims.

This invention relates to the manufacture of alternating electriccurrent rectifiers of the dry surface contact type comprising a body ofmetal having a compound of the metal formed directly 5 thereon and moreparticularly rectifiers of the copper oxide type.

Rectifier elements of this character may be manufactured as has hithertobeen proposed by heating metal blanks in a suitable atmosphere 3.0 at asuitable temperature for a suitable period of time to form a compound ofthe metal thereon, as for example, by heating copper blanks in anoxidising atmosphere to form cuprous oxide on the surface of the metal,and then transferring the blanks immediately from the oxidising furnaceto an annealing furnace maintained at a lower annealing temperature soas to cool the blanks to this lower temperature and then immediately, orafter the blanks have been maintained at the annealing temperature for apredetermined relatively long period of time, removing the blanks fromthe annealing furnace and suddenly cooling or quenching them in coldwater or a current of cold air.

According to the present invention, however, the blanks after beingheated or subjected to the oxidising temperature as referred tohereinbefore are arranged to be cooled, by exposing them to cold air forinstance, to a temperature intermediate the oxidising and annealingtemperatures before being subjected to the annealing temperature, theintermediate temperature being preferably only a few degrees above theannealing temperature.

It is found that, by delaying the transfer of the oxidised blanks fromthe oxidising to the annealing furnace in this way, instead ofimmediately transferring the blanks from the oxidising to the annealingfurnace as in previously known processes, the forward resistance of therectifier elements is reduced without correspondingly reducing thereverse resistance, which as will be readily understood constitutes animportant advantage.

, In the case of copper oxide rectifiers the delay period required intransferring a normal or usual furnace charge of oxidised blanks fromthe oxidising to the annealing furnace may, for example, be about oneminute, the subsequent annealing 59 period prior to quenching being ofnormal duration, for instance ten minutes.

'The reduction of the forward resistance thus obtained is similar tothat which would be obtained by transferring the oxidised blanks imgz;mediately from the oxidising furnace to the annealing furnace andmaintaining them as has hitherto been proposed at the annealingtemperature for a relatively long period of time, for instance 30minutes, but in this latter case the reverse resistance also would becorrespondingly 5 reduced which as will be evident is undesirable.

However by delaying the transfer for one minute as explainedhereinbefore the reverse resistance of the elements is the same as itwould have been if the oxidised blanks had been sub- 10 jected to theannealing temperature for ten minutes without the intermediate delay andthus in accordance with the invention a reduction of the forwardresistance is obtained Without a corresponding undesirable reduction of\thereverse 18 resistance, it being understood'that the reverseresistance is reduced progressively as the annealing period isincreased.

Moreover by delaying the transfer from the oxidising to the annealingfurnace in order to 20 reduce the forward resistance in accordance withthe invention a considerable reduction of the time required for theannealing process is effected as compared with the previously proposedprocess referred to in which the oxidised blanks had to 25 be maintainedin the annealing furnace for a relatively long period of time.Furthermore the delay between the oxidising and annealing processesfacilitates the provision of a continuous furnace plant for theproduction of rectifier ele- 30 ments, as the isolation of the period oftime required for oxidation from the period of time required forannealing by the delay period makes the manufacture cycle elastic, aseither the oxidation time or the annealing time can easily be 5 variedindependently of the other.

It will be understood that the invention is not limited to the delay andannealing periods hereinbefore given only by way of example, .theseperiods being capable of being varied to suit par- 40 ticular conditionsor requirements. I

Having now particularly described and ascertamed the nature of my saidinvention and in what manner the same is to be performed, I declare thatwhat I claim is: 45

The method of manufacturing a copper oxide rectifier which consists insubjecting a copper blank to an oxidizing temperature to form an oxidelayer thereon, removing the blank from the oxidizing temperature andexposing it to cold air for about one minute, and then subjecting theblank to an annealing temperature.

2- The method of manufacturing a copper oxide rectifier which consistsin subjecting a copper blank to an oxidizing temperature to form anoxide layer thereon, removing the blank from the oxidizing temperatureand exposlnc it to cold air for about one minute. and then subjectingthe blank to an annealing temperature for about ten minutes.

3. In the process of manufacturing a copper oxide rectifier wherein acopper blank is first oxidized by subjecting it to an oxidizingtempcrature in an oxidizing atmosphere and is subaequently annealed ata. lower temperature, the step which consists in permitting the oxidizedblank to cool in cold air Just prior to annealing it !or a time which issuiiicient to cool it to a temperature only a iew degrees above theannealing temperature.

ROGER HARRY CUBI'IT.

